Air flow restrictor for gun port



March 20, 1956 J ALLEN 2,738,710

AIR FLOW RESTRICTOR FOR GUN PORT Filed June 6, 1951 2 Sheets-Sheet l INVENTOR JOHN xv. 44 4 51V,

ATTO\NEY March 20, 1956 J ALLEN 2,738,710

AIR FLOW RESTRICTOR FOR GUN PORT Filed June 6, 1951 2 Sheets-Sheet 2 INVENTOR JOHN A. 194 LE/V,

TTORNEY 2,738,710 AIR FLOW RESTRICTOR FOR GUN PORT John H. Allen, Baltimore County, Md., assignor to The Glen L. Martin Company, Middle River, Md., a corporation of Maryland Application June 6, 1951, Serial No. 230,222 7 Claims. (Cl. 8937.5)

This invention relates to the prevention of ram air flow into the gun ports of an aircraft, and more particularly to the provision of a flexible device between the barrel of a gun mounted in an aircraft, and the wall of the blast tube through which the gun protrudes, in order to obstruct the flow of air into the gun compartment.

In high speed aircraft carrying guns mounted within the structure of the aircraft, it is necessary to provide means between the gun barrel and the walls of its blast tube to prevent ram air from entering around the gun barrel and developing undesirable high pressures in the gun compartment during flight. At the same time, it is desirable to allow a sufficient quantity of air to flow along the gun barrel to cool it. In addition, any such means used between the gun barrel and the blast tube must be flexible enough to allow relative movement between the gun barrel and the blast tube so that the gun may be boresighted, and so that vibration of the gun barrel within the tube will not damage the obstructing means.

It is the object of this invention to provide a device, which, while effectively preventing the buildup of undue pressures in the gun compartment, will allow suificient air to flow along the gun barrel to cool it.

It is a further object of this invention to provide a device for obstructing the air flow into the blast tube and along the gun barrel, the device being flexible enough to allow relative movement between the gun barrel and the blast tube, thereby permitting the gun to be boresighted without impairing the effectiveness of the obstructing device, and eliminating the possibility of damage to the obstructing device or the gun caused by vibration of the gun while it is being fired.

These and further objects will become apparent from the following description taken in connection with the accompanying drawings.

In the drawing:

Figure l is a perspective view of the nose of an aircraft carrying guns mounted to protrude through gun ports in the nose of the aircraft with a portion of the structure cut away to show the obstructing device mounted within the blast tube.

Figure 2 is a cross section of the gun barrel taken be hind the blast tube looking forward.

Figure 3 is a section taken on line 3-3 of Figure 2.

Figures 4 and are section views similar to Figure 3 and showing two modifications of the invention.

In Figure 1 is shown the nose of an aircraft 1 in which are mounted guns 2 adapted to be fired through suitable openings 3 provided in the nose of the aircraft. Since the gun barrels 4 do not project beyond the nose of the aircraft, generally cylindrical blast tubes 5 are provided, rigid with the aircraft nose structure, the tubes extending rearwardly from the openings 3 and surrounding the forward portion of the barrels 4 to prevent damage to the aircraft structure due to the gun blasts. The guns are ordinarily carried within a suitable gun compartment 6 formed by the nose portion of the aircraft, which comd States at 2,738,710 Patented Mar. 20, 1956 partment, while not completely airtight, nevertheless is so constructed as to permit but limited leakage of air therefrom. As a result, unless means are provided to prevent such action, when the airplane is flying at high speeds ram air will be forced through the blast tube 5 far more rapidly than it can leak therefrom, with the result that the pressure will soon build up within the compartment to substantially the full ram pressure, tending to blow olf access cover plates such as 14 and 15 and to place undue strain on the structure.

To obstruct the flow of ram air into the blast tubes 5, a conical shaped closely wound helical spring 6 is mounted within each tiube. The two largest coils of the spring are of the same diameter and are spaced apart to provide for attachment to blast tube 5 as shown in Figures 2 and 3, by means of retainer ring 7 and a plurality of bolts 8, secured by nuts 9, the bolts 8 passing between the two spaced coils before mentioned. The small end of spring 6 is of such a diameter as to provide a predetermined annular gap 10 between the small end of the spring and the gun barrel 4, the gap acting as an orifice to maintain sufiicient pressure drop in the air flow into the gun compartment 6 to prevent the buildup of undesirable high pressures, at the same time providing sufficient air fiow to cool the gun. When the gun is being fired, it may vibrate sufiiciently to strike the spring 6, but the resiliency of the spring will prevent damage to either the gun or the spring. However, if a rigid barrier were used to impede the air flow, vibration of the gun might damage the edges of the opening in the barrier, possibly enlarging the opening and thereby reducing the pressure drop in the air flow into the gun compartment 6, thus allowing an undesirable pressure buildup.

In an installation in which it is not necessary to provide air flow for cooling the gun, the small end of the spring may be of such a diameter as to fit snugly around the barrel of the gun as shown in Figure 4, thus providing a seal to prevent any appreciable flow of air into the gun compartment. Referring to Figure 4, spring 11 is shown with the two smallest coils 12 being of the same diameter and adapted to fit closely around the gun barrel 4, thus providing a good fit between the spring and the gun barrel.

If it is desired to allow more air flow than would be permitted by the installation shown in Figure 3, but still provide a partial obstruction to air flow into the gun compartment 6, spring 16 may be made with its coils loosely wound as shown in Figure 5, providing a. continuous spiral gap 13 of predetermined width between the coils of the spring, thus allowing the desired volume of air to flow through blast tube 5 into the gun compartment 6.

In all of the above described installations, the flexibility of the spring will allow relative movement between gun barrel 4 and the blast tube 5, thereby permitting movement of the gun for boresighting, and allowing vibration of the gun barrel within the blast tube while the gun is being fired, without danger of damage to the spring, or permanent alteration of the size and configuration of the cooling air aperture.

While but three forms of the invention have been specificially shown and described, it is obvious that many changes can be made without departing from the spirit and scope of the invention as defined by the following claims.

I claim as my invention:

1. In an aircraft, a gun having a forwardly trained barrel mounted within said aircraft, means forming an aperture in the surface of said aircraft, the axis of said gun barrel being in substantial alignment with said aperture, and means for obstructing air flow into said aircraft through said aperture consisting of a forwardly con- 'ergent, conical shaped helical spring surrounding said gun barrel, and having its rear end secured to said aperure forming means.

2. In an aircraft, a gun having a forwardly trained Jarrel mounted within said aircraft, means forming a blast .ube, the forward end of said tube forming an aperture n the surface of said aircraft, said gun barrel extending from the interior of said aircraft into said tube, and a :losely wound forwardly convergent conical shaped spring mounted Within said blast tube and surrounding said gun barrel, forming an annular space between the smaller end of said spring and the gun barrel, the larger rearward end of said spring being fastened to the interior of said blast tube.

3. In an aircraft, a gun having a forwardly trained barrel mounted within said aircraft, means forming a blast tube, the forward end of said tube forming an aperture in the surface of said aircraft, the other end extending into the interior of said aircraft, said gun barrel extending from the interior of said aircraft into said tube, and means forming an obstruction mounted between said gun barrel and the wall of said tube to prevent air flow through said tube into the interior of said aircraft, said means comprising a forwardly convergent conical shaped helical spring surrounding said gun barrel, the large rearward end of said spring being fastened to the interior of said blast tube, the small forward end fitting snugly around said gun barrel.

4. In an aircraft, a gun having a forwardly trained barrel mounted within said aircraft, means forming a blast tube, the forward end of said tube forming an aperture in the surface of said aircraft, said gun barrel extending from the interior of said aircraft into said tube, and a loosely wound forwardly convergent, conical shaped coil spring mounted within said aperture and surrounding said gun barrel, the space between the coils of said spring forming a spiral shaped opening to allow a predetermined quantity of air to flow through said spiral opening past said gun barrel.

5. In an aircraft, a gun having a forwardly trained barrel mounted within said aircraft, means forming a blast tube, the forward end of said tube forming an aperture in the surface of said aircraft, said gun barrel extending from the interior of said aircraft into said tube, and means mounted within said tube and surrounding said gun barrel to obstruct the air fiow through the tube into the interior of said aircraft, said means comprising a forwardly convergent conical shaped helical spring.

6. In an aircraft, a gun having a forwardly trained barrel mounted within said aircraft, means forming an aperture in the surface of said aircraft, the axis of said gun barrel being in substantial alignment with said aperture, and a forwardly convergent conical shaped helical spring attached at its rear end to said aircraft and surrounding said gun barrel to form an obstruction to air fiow into said aircraft through said aperture.

7. in an aircraft, a gun having a forwardly trained barrel mounted within said aircraft, means forming a blast tube, the forward end of said tube forming an aperture in the surface of said aircraft, said gun barrel extending from the interior of said aircraft into said tube, and means for obstructing air fiow into said aircraft along said gun barrel comprising a forwardly convergent conical shaped helical spring mounted interiorly of said blast tube and having its larger end in peripheral juxtaposition with the interior wall of said blast tube, said spring surrounding said gun barrel and extending inwardly theretoward so that the smaller end of said spring lies closely adjacent said gun barrel.

References Cited in the file of this patent UNITED STATES PATENTS 2,263,465 Levendoski Nov. 18, 1.941 2,291,867 Birkigt Aug. 4, 1942 2,338,950 Linke et al. Jan. 11, 1944 2,514,495 Johnson July 11, 1950- 2,573,434 Graham Oct. 30, 1951 

